flag user

Question:

#
cos(156 degrees) cos(35 degrees) plus sin(156 degrees) sin(35 degrees)?

### Tag

flag user

We have the formula: cos(a - b) = cos a . cos b + sin a . sin b

Then:

cos(156 degrees) cos(35 degrees) plus sin(156 degrees) sin(35 degrees) = cos(156 degrees - 35 degrees) = cos (120 degrees) = - cos (60 degrees) = - 1/2

Then:

cos(156 degrees) cos(35 degrees) plus sin(156 degrees) sin(35 degrees) = cos(156 degrees - 35 degrees) = cos (120 degrees) = - cos (60 degrees) = - 1/2

flag user

Cos(156)Cos(35)+Sin(156)Sin(935)= -0.5150 Which if we round to a fraction will turn to -1/2. to solve this problem you just have to plot it in in your Graphic calculator.

P.s. Do n0t forget the (PARENTHESIS)

P.s. Do n0t forget the (PARENTHESIS)

flag user

we know that : cos x . cos y +sin x . sin y = cos ( x - y) .

comparing the problem with the above formula ;

we get : x = 156 degrees , y = 35 degrees

therefore,

cos(156 degrees) cos(35 degrees) plus sin(156 degrees) sin(35 degrees)

= cos(156 degrees - 35 degrees)

= cos (120 degrees)

= cos (180 degrees- 120 degrees)

= - cos (60 degrees) [ since cos in second quadrant is negative i.e from 90 degrees to 180 degrees]

= - 1/2

therefore,

cos(156 degrees) cos(35 degrees) plus sin(156 degrees) sin(35 degrees) = - 1/2 = - 0.5

comparing the problem with the above formula ;

we get : x = 156 degrees , y = 35 degrees

therefore,

cos(156 degrees) cos(35 degrees) plus sin(156 degrees) sin(35 degrees)

= cos(156 degrees - 35 degrees)

= cos (120 degrees)

= cos (180 degrees- 120 degrees)

= - cos (60 degrees) [ since cos in second quadrant is negative i.e from 90 degrees to 180 degrees]

= - 1/2

therefore,

cos(156 degrees) cos(35 degrees) plus sin(156 degrees) sin(35 degrees) = - 1/2 = - 0.5