Question

cos(x+pi/2) = -sin x
help! i need somebody.. help! not just anybody

Answer 1

Apply cos (A+B) formula
know what it is ?

Answer 2

\(\cos(A+B) = \cos A\cos B - \sin A \sin B \)

Answer 3

A = x
B =pi/2

Answer 4

so,
cos x cos pi/2 - sin x sin pi/2

Answer 5

yes
what are
cos pi/2 = ..
sin pi/2 = .. ?

Answer 6

do they equal each other?

Answer 7

no...
cos pi/2 = 0
sin pi/2 = 1
do you have unit circle with you ?

Answer 8

yes

Answer 9

then look for pi/2 angle in it.
what are the co-ordinates when angle is pi/2 radians or 90 degrees

Answer 10

(0,1)

Answer 11

correct,
those are read as
\((\cos \theta , \sin \theta)\)

and since \(\theta = \pi/2 \)
we get
\((\cos \pi/2 , \sin \pi/2 )=(0,1)\)

Answer 12

thats why
cos pi/2 = 0
and sin pi/2 = 1
now plug these in your equation

Answer 13

cos x 0 - sin x 1 ?

Answer 14

correct!
simplify it

Answer 15

- sin x

Answer 16

\(\huge \checkmark \)

Answer 17

ahh! you're a life saver!

Answer 18

^_^

Answer 19

thank you sososososososososososo much!

Answer 20

welcome sososososososososososo much!

Answer 21

:)