Substitute into Identity: Substitute the value of (17/20)2 into the Pythagorean identity.289/400+cos2(θ1)=1
Solve for cos2(θ1): Solve for cos2(θ1).cos2(θ1)=1−400289cos2(θ1)=400400−400289cos2(θ1)=400400−289cos2(θ1)=400111
Find cos(θ1): Find the square root of cos2(θ1) to get cos(θ1). Since θ1 is in Quadrant I, cos(θ1) is positive. cos(θ1)=400111cos(θ1)=400111cos(θ1)=20111
More problems from Find trigonometric ratios using multiple identities