how do i turn cos45 into a surd? or anyother function for that matter? In part of the equation below;

-2 x (x+2) x 4 x cos45

How do i find x?

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- Oct 9th 2008, 07:02 AMFlexibleturning trigonomic functions into surds
how do i turn cos45 into a surd? or anyother function for that matter? In part of the equation below;

-2 x (x+2) x 4 x cos45

How do i find x? - Oct 9th 2008, 01:08 PMMoo
Hello,

cos(45) is supposed to b a known value, that is sqrt(2)/2

this can be "proved" this way :

cos(45)=sin(45) (because cos(90-x)=sin(x))

we know that cosē(x)+sinē(x)=1

hence 2cosē(x)=1

cosē(x)=1/2

cos(x)=+ or - 1/sqrt(2)=+ or - sqrt(2)/2

since 45 is in the first quadrant, its cosine is positive. hence it's sqrt(2)/2