Teacher2Teacher Q&A #193

Teachers' Lounge Discussion: Trigonometry Ratios

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From: Loyd

To: Teacher2Teacher Public Discussion
Date: 2004012712:39:57
Subject: Re: Trig Delema! am i crazy???

On 2004012620:35:31, Ross wrote: > >OK. you have a big triangle...the left angle is 25...the right is >15...the top is 140... >you have a line coming from the top angle going down and touching the >bottom...it's perpendicular (the angles where it touch make 90 >degrees)...on the left triangle: the bottom side is 1.5...on the right >triangle: the bottom side is 3.5 ... >you want to solve for the length of the line coming from the top going >down (that you just drew)... > >if you use the left triangle: >1.5 x tan(25) = .6995 > >if you use the right triangle: > >3.5 x tan (15) = .9378 > >why??? WHY??? shouldn't they be the same??? > Try drawing the triangle to scale and you will see that this is impossible to have the base divided into 1.5 and 3.5 sections for the angles you gave. Once you made the right hand side of the base equal to 3.5, then the only way for the other part of the base to be 1.5 would be if the angle on the left was on the order of 32 degrees and then you wouldn't preserve the 25, 140, 15 degree relationship You apparently chose both dimensions for the base. You can choose one of them and calculate the other. If is important to preserve the 25, 140, 15 degree relation ship then you will have to calculate the dimensions of the left side of the base if you choose 3.5 for the right hand side of the base.

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