Find the exact values of sin 2u, cos 2u, and tan 2u using the double-angle formulas. sec u = −2, π/2 < u < π

now... we have -2/1   but... which one is the negative?   well
we know the angle is " π/2 < u < π", that simply means, the 2nd quadrant
well, in the 2nd quadrant, the "x" or adjacent side is negative, so the adjacent side is then -1

now, let us use the pythagorean theorem, to get the opposite side



now..which one though?  well, recall, we're in the 2nd quadrant, in the 2nd quadrant "y" or the opposite side, is positive, so is √(3) then

now... let's plug in those values in the double-angle identities then





simplify away

Answer to your question: a. the fundamental theorem of algebra tells you that the equation will have two complex roots since the degree of the polynomial is 2. the roots are ​ x=1±i7√2 .number of roots=degree of polynomialhere, degree of polynomial is 2 so number of roots will be 2.hope it *_*