# Math Help - [SOLVED] trig question

1. ## [SOLVED] trig question

so had my AS core 1 exam today - dont think i did very well, bugger. anyway the question is...

You are given that $tanA=\frac{1}{2}$ and the angle A is acute. show without using a calculator that $cos^2A=\frac{4}{5}$

ta

2. ## Re :

Originally Posted by coyoteflare
so had my AS core 1 exam today - dont think i did very well, bugger. anyway the question is...

You are given that $tanA=\frac{1}{2}$ and the angle A is acute. show without using a calculator that $cos^2A=\frac{4}{5}$

ta

Note that tan A is in the first quadrant . Draw a triangle ..

From there you will be able to find that $cos A = \frac{2}{\sqrt 5}$

Squarring it , you should get the results ...

3. ## sorry to be...

....stupid but i dont understand this as of yet and require it to be explained more if at al possible, the book is just confusing me!

ta

4. ## Re :

Originally Posted by coyoteflare
....stupid but i dont understand this as of yet and require it to be explained more if at al possible, the book is just confusing me!

ta

Alright , it is ok . Firstly , do u know that when you are given the value of a trigo function , ie
$tanA=\frac{1}{2}$
you can draw a triangle and find cos A and sin A as well ?
If u do , well , the question tells us that A is an acute ( smaller than 90 ) , so we know that tan A is in the first quadrant and everything is positive here .

Note that $(cos A)^2=cos^2A$