Respuesta :
Answer:
See below.
Step-by-step explanation:
1. (1 / 2)[cos(a – b) – cos(a + b)]
= 1/2 ( cosa cosb + sina sinb - (cosa cosb - sina sinb)
= 1/2 ( cosa cosb - cosa cos b + sina sinb + sina sinb)
= 1/2 ( 2 sina sinb)
= sina sinb.
(I used the 2 identities cos(a - b) = cosa cosb + sina sinb) and
cos (a + b) = cosa cosb - sina sinb.)
2. sin (π/2 - x) = sin (π/2) cos x - cos(π/2) sin x
= 1 * cos x - 0 * sinx
= cosx - 0
= cos x.
(I used the identity sin(a - b) = sina cosb - cosa sinb
and the fact that sin(π/2) = 1 and cos (π/2) = 0. )
Answer:
1. sin a sin b = (1 / 2)[cos(a – b) – cos(a + b)]
Calculation:
Taking L.H.S. of above equation
(1 / 2)[cos(a – b) – cos(a + b)]
= (1 / 2) [ (cos a cos b + sin a sin b) - (cos a cos b - sin a sin b)]
{∵ cos(a – b) = cos a cos b + sin a sin b & cos(a + b) = cos a cos b - sin a sin b}
= (1 / 2) [ cos a cos b + sin a sin b - cos a cos b + sin a sin b]
= (1 / 2) [2 sin a sin b]
= sin a sin b
2. sin((π / 2) – x) = cos x
Calculation:
sin((π / 2) – x) = sin (π / 2) cos x - cos (π / 2) sin x
{∵sin(a - b) = sin a cos b - cos b sin a
& sin (π / 2) = 1 & cos (π / 2) = 0}
= 1 × cos x - 0 × sin x
= cos x
