Given that sin theta cos theta =7/50sinθcosθ=750 and 0^0 < theta < 90^000<θ<900. Find the value of cos thetacosθ.?

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2 Answers
Jun 22, 2018

7/(5*sqrt(2)),1/(5*sqrt(2))752,152

Explanation:

Solving the equation
sin(theta)*cos(theta)=7/50sin(θ)cos(θ)=750
in the given interval we get

x_1=-2arctan(7-5sqrt(2))x1=2arctan(752)

x_2=2arctan(1/7(5sqrt(2)-1))x2=2arctan(17(521))
so we gat

cos(x_1)=7/(5sqrt(2))cos(x1)=752

cos(x_2)=1/(5sqrt(2))cos(x2)=152

Jun 22, 2018

8^@13, 81^@87813,8187

Explanation:

sin t.cos t = 7/50sint.cost=750
Use trig identity: sin 2t = 2sin t.cos t
In this case:
sin t.cos t = (sin 2t)/2 = 7/50sint.cost=sin2t2=750
sin 2t = 15/50 = 7/25 sin2t=1550=725
Calculator and unit circle give 2 solutions for 2t:
2t = 16^@262t=1626, and 2t = 180 - 16.26 = 163^@742t=18016.26=16374
a. 2t = 16.26 + k360
t = 8^@13 + k180^@t=813+k180
b. 2t = 163.74 + k360
t = 81^@87 + k180^@t=8187+k180
Answers for (0, 90)
8^@13, 81^@87813,8187
cos (8.13) = 0.99
cos (81.87) = 0.14