Question

if A=60° and B=30° prove
$\cos ( A - B ) = \cos A \cos B + \sin A \sin B$
​

Answer 1

Answer:

LHS =cos(A+B)=cos(60

o

+30

o

)=cos90

o

=0

RHS =cosAcosB−sinAsinB

=cos60

o

cos30

o

−sin60

o

sin30

o

=

2

1

×

2

3

−

2

3

×

2

1

=

4

3

−

4

3

=0

∴ LHS = RHS

Step-by-step explanation:

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