Question

sin ( 90 + theta ) = cos theta

prove^

Answer 1

i guess it depends on what you can use
if you can use the addition angle formula, that would work
if not maybe with a triangle you can see it

Answer 2

i want to do with the triangle one but m wondering how will you show (90+theta) in a right angled triangle?

Answer 3

yes but that is 90 - theta? do 90-theta has any relation with 90 + theta ?

Answer 4

\[\cos(x)=\frac{a}{c}=\sin(90-x)=-\sin(x-90)\]
\[=\sin(x-90+180)=\sin(x+90)\]

Answer 5

how : -sin(x-90) = sin(x-90+180) ?

Answer 6

third equal sign because sine is odd, fourth because \(\sin(x)=-\sin(x+180)\)

Answer 7

Gotcha now, thanks a lot!

Answer 8

your on the other side of the unit circle

Answer 9

yw

Answer 10

hey, how you did this step? :
\[\large{-\sin(x-90) = sin(x-90+180) }\]
?

Answer 11

@satellite73 did you subtract sin(180) both sides?

Answer 12

i added 180 inside because \(\sin(x)=-\sin(x+180)\)

Answer 13

oh k , got it!