# Trig Proof

• Aug 28th 2010, 02:43 PM
jacs
Trig Proof
I have a trig proof i have come at from every way i can think of and just can't make it work

If a/sin A = b/cos A, show that sin A cos A = (ab)/(a^2 + b^2)

thanks
• Aug 28th 2010, 03:18 PM
Quote:

Originally Posted by jacs
I have a trig proof i have come at from every way i can think of and just can't make it work

If a/sin A = b/cos A, show that sin A cos A = (ab)/(a^2 + b^2)

thanks

$\displaystyle\frac{a}{SinA}=\frac{b}{CosA}\Rightar row\ \frac{a}{b}=\frac{SinA}{CosA},\ \frac{b}{a}=\frac{CosA}{SinA}$

Then

$\displaystyle\frac{a}{b}+\frac{b}{a}=\frac{a^2+b^2 }{ab}$

Work that out and invert the result.
• Aug 28th 2010, 03:38 PM
jacs
Thanks, figured it out now. Never would have thought to do it that way on my own!