Practicing Success
If sin θ(2sin θ + 3) = 2, 0° < θ < 90°, then what is the value of (sec2 θ +cot2 θ - cos2 θ) ? |
$\frac{13}{3}$ $\frac{31}{12}$ $\frac{7}{2}$ $\frac{43}{12}$ |
$\frac{43}{12}$ |
sin θ(2sin θ + 3) = 2 2sin² θ + 3sin θ - 2 = 0 2sin² θ + 4sin θ - sin θ - 2 = 0 2sin θ ( sin θ + 2 ) - 1 ( sin θ + 2 ) = 0 (sin θ + 2 ) . (2sin θ - 1 ) = 0 sin θ + 2 = 0 is not possible. So, 2sin θ - 1 sin θ = \(\frac{1}{2}\) { we know, sin30º = \(\frac{1}{2}\) } so, θ = 30º Now, ( sec2 θ +cot2 θ - cos2 θ ) = ( sec2 30º+cot2 30º - cos2 30º ) = \(\frac{4}{3}\) + 3 - \(\frac{3}{4}\) = \(\frac{16 + 36 - 9 }{12}\) = \(\frac{43 }{12}\) |