If sinθ=0.8 and θ lies in 2ndquadrant. Find the value of cosθ. Given, sin2θ+cos2θ=1
A
0.6
No worries! We‘ve got your back. Try BYJU‘S free classes today!
B
−0.6
Right on! Give the BNAT exam to get a 100% scholarship for BYJUS courses
C
−0.8
No worries! We‘ve got your back. Try BYJU‘S free classes today!
D
0.8
No worries! We‘ve got your back. Try BYJU‘S free classes today!
Open in App
Solution
The correct option is B−0.6 We have, sinθ=0.8 And we have, sin2θ+cos2θ=1⇒cos2θ=1−sin2θ⇒cos2θ=1−0.82=0.36⇒cos2θ=(0.6)2⇒cos2θ−(0.6)2=0⇒(cosθ−0.6)(cosθ+0.6)=0⇒cosθ=0.6,−0.6
Since θ lies in 2nd quadrant and we know cosθ is negative in 2nd quadrant. ∴cosθ=−0.6