61 cos10cos 61 cos10cos209 sin10cos70 10 cos Solutiongiven

61. cos(10)cos 61. cos(10)cos(209) + sin(-10°)cos(70°) 10 cos

Solution

given

cos( 10⁰ ) cos( 20) + sin( -10) cos(70 )

since sin(-x) = - sinx

so sin(-10) = - sin( 10 )

givne equation becomes

cos(10 ) cos(20) - sin ( 10 ) cos(90 - 20 )

==> cos(10) cos(20 ) - sin(10) sin(20 )

this looks like cos( a + b) = cosa cosb - sina sinb

==> cos( 10 + 20)

==> cos( 30)

==> 0.15425