How do you evaluate the expression sin(u+v)sin(u+v) given sinu=3/5sinu=35 with pi/2<u<pπ2<u<p and cosv=-5/6cosv=56 with pi<v<(3pi)/2π<v<3π2?

1 Answer
Dec 3, 2016

sin(u+v)=(-15+4sqrt11)/36=-0.0481sin(u+v)=15+41136=0.0481

Explanation:

As sinu=3/5sinu=35 and domain of uu is given by pi/2 < u < piπ2<u<π i.e. uu is in second quadrant and cosucosu is negative and

cosu=-sqrt(1-(3/5)^2)=-sqrt(1-9/25)=-sqrt(16/25)=-4/5cosu=1(35)2=1925=1625=45

Further as cosv=-5/6cosv=56 with pi < v < (3pi)/2π<v<3π2, hence vv is in third quadrant and sinvsinv is negative and

sinv=-sqrt(1-(-5/6)^2)=-sqrt(1-25/36)=-sqrt(11/36)=-sqrt11/6sinv=1(56)2=12536=1136=116

Now sin(u+v)=sinucosv+cosusinvsin(u+v)=sinucosv+cosusinv

= 3/5xx(-5/6)+(-4/5)xx(-sqrt11/6)35×(56)+(45)×(116)

= (-15)/30+(4sqrt11)/301530+41130

= (-15+4sqrt11)/3615+41136

= (-15+4xx3.317)/36=-1.732/36=-0.048115+4×3.31736=1.73236=0.0481