Algebra Terms: 'Evaluate' and 'Simplify'Date: 7/30/96 at 14:38:11 From: Ralph Ware Subject: Algebra Terms Dear Dr. Math: I am a 43-year-old man entering college this fall for the first time. One of my required courses is Elementary Algebra. It has been 25 years since I've seen an algebra problem and I didn't exactly set the world on fire with my mathematical ability back then, even though I passed both Algebra I and II in high school. The college has sent me a sample list of problems I must be able to work in order to remain enrolled in the course. Some of the mathematical skills I learned in elementary and high school remain familiar because I use them in solving every day problems. But I am unfamiliar with some of the terms used in the list. I have found the "Ask Dr. Math" portion of the Math Forum to be very helpful in getting back into the swing of things. Even though I am a lot older than most of the students who write you, I hope that you will help me with my questions, too. 1. Evaluate: 3-{2-3(2-7)} What does "Evaluate" mean? 2. Simplify: -3x{7-(3x-5)} What does "Simplify" mean? Any help you can give me will be greatly appreciated. Thank you. Ralph Ware Date: 7/30/96 at 15:33:7 From: Doctor Robert Subject: Re: Algebra Terms Evaluate means to "find the value" of. It is similar to the old question, "what is 10 plus 4?" Evaluate (10+4) should evoke the same answer. To answer your particular question I'll work it out step by step: 3-(2-3(2-7)) = 3-(2-3(-5))=3-(2+15) = 3-17 = -14. When evaluating an expression, you must pay attention to the ORDER OF OPERATIONS. Simplify means to make more simple. In your example you cannot evaluate the expression for you are not told the value of x. However, you can, using the order of operations, simplify the expression. -3x(7-(3x-5)) = -3x(7 - 3x + 5) = -3x(12-3x) = -36x + 9x^2. I hope that this helps. -Doctor Robert, The Math Forum Check out our web site! http://mathforum.org/dr.math/ Date: 7/30/96 at 15:42:15 From: Doctor Pete Subject: Re: Algebra Terms "Evaluate" means that a particular value is desired for the answer. In other words, they want a single number. "Simplify," on the other hand, means "to make simpler," or to reduce the number of symbols used while retaining equality. So for "simplify," they don't want a single number, but instead they're looking for something like "4x" or "3x+2" - which is as short and sweet as you can make things. So to "evaluate" the first problem, we start from the inside and work our way outwards: 3-{2-3(2-7)} = 3-{2-3(-5)} = 3-{2-(-15)} = 3-{2+15} = 3-17 = -14 . Notice the answer is a number (in this case, it is negative), not an expression with a variable in it. For the second problem, we have -3x{7-(3x-5)} = -3x{7-3x+5} (distribute the minus sign) = -3x{12-3x} 2 = 9x -36x . <-- this is "nine x squared minus thirty-six x" Now, although this is probably the "simplest" form, it isn't the way I would want to write it. I'd rather say this is = 9x(x-4) , because it tells me more. It says, "Well, if x=4, the expression is 0." But in general, "simple" means fewer parentheses and groupings, as well as fewer operations (plus, minus, multiply, divide) used. However, in general, it doesn't really matter whether somebody says "simplify" or "evaluate." They just want you to make the expression as short or compact as possible. The technical difference is that "simplify" usually refers to an expression with variables, where you (usually) can't get a single number out of it, while you can with "evaluate." -Doctor Pete, The Math Forum Check out our web site! http://mathforum.org/dr.math/ Date: 8/1/96 at 16:59:29 From: Doctor Mike Subject: Re: Algebra Terms Hello Mr. Ware, Your questions are appropriate. We cover whatever COULD BE in grades K through 12. College teachers don't mind older students. In fact, students with more maturity who take the subject seriously may even have an advantage, since most teachers also tend to take their subject seriously. Have fun. If what I'm writing below makes a lot of sense, and what you learned from High School starts coming back to you more and more, then I am glad to have helped with that. But if it is still pretty confusing then go ahead and take a lower course that will include a lot more review. I'm pretty sure that these questions "in order to stay enrolled in the course" are just an informal "placement test" to make sure you are placed in the right course to correspond to your background. They want you to succeed. Let's take "Evaluate" first. That just means to find out what that long expression is equal to. You have to use things you learned in algebra, like [1] Always do the operation inside the parentheses first, [2] A negative number times a negative number is a positive number, [3] The distributive law for "multiplying out" stuff, like a*(b+c) = a*b + a*c , etc. There are non-obvious forms of that rule, like the following: a*(b-c) = a*b - a*c -1*(b+c) = -b - c -1*(b-c) = -b + c -(b-c) = -b + c etc. , etc., etc. I'll give you a step-by-step for your example so you get the picture: (a) (2-7) gives -5 (b) -3 times -5 from step (a) gives 15 (c) 2 plus 15 from step (b) gives 17 (d) 3 minus 17 from step (c) gives -14 so -14 is the numerical value of that expression; we "Evaluated" it. Now for "Simplify". This is not as straightforward as the other since various people may have different ideas of what is more simple than what else. But everybody agrees that -3x{7-(3x-5)} could be made simpler. Keep in mind here is that "x" represents some number. You do not know what that number is, but you are guaranteed that you can do anything with "x" that you can do with ANY number. Here is a step-by-step for what I would do for this one : (A) -(3x-5) is the same as -3x + 5 from one of the versions of the distributive law. (B) So, what is within the braces is 7 - 3x + 5 . (C) If you want, you can think of this as 7 + (-3x) + 5 to show that this is just 3 numbers added together, and you know that numbers can be added in any order, so re-write it as 7 + 5 + (-3x) . (D) Simplify the (C) expression to just 12 - 3x . (E) So now the original expression amounts to -3x times 12-3x . (F) How could that be simplified? Here is where we get into the nebulous area of interpretation. Since A*B = (-A)*(-B) it follows that -3x times 12-3x is the same as 3x times 3x-12 . That looks simpler to me since the minus sign is gone from 3x. (G) Some would think (3x)*(3x-12) is a nice simple factored form, whereas others would prefer 9x^2 -36x in multiplied out form. NOTE: I'm using x^2 for x squared. (H) People who preferred factored results might want to go the other direction and factor out 9x to get (9x)*(x-4). This is what I would prefer, but if your prof has different ideas about it, keep in mind who will grade your exams! I hope this is exactly what you needed. If not please write back. -Doctor Mike, The Math Forum Check out our web site! http://mathforum.org/dr.math/ |
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