Question

Easy question
please help...

Answer 1

oekj
\[\rm If~ x=\cos\theta-rsin\theta,~y=\sin\theta+rcos\theta\\ Then~prove~that~\frac{ dr }{ dx }=\frac{ x }{ r }\]

Answer 2

Nevermind, I am also doing trigonometric proofs and I'm suffering too :(

Answer 3

@UnkleRhaukus @freckles :)

Answer 4

ok we square and add both the equations
u get this-\[x^2+y^2=1+r^2\]\[r=\sqrt{x^2+y^2-1}\]differentiating-\[\frac{ dr }{ dx }=\frac{ d }{ dx }\sqrt{x^2+y^2-1}\]\[\frac{ dr }{ dx }=\frac{ 1 }{ 2 }\frac{ 2x }{ \sqrt{x^2+y^2-1 }}\]\[\frac{ dr }{ dx }=\frac{ x }{ r }\]

Answer 5

perfect

Answer 6

:)

Answer 7

thanks (: