(A)y=x2+2x+4x+2
⇒x2+(2−y)x+4−2y=0
⇒y2+4y−12≥0
y≤−6 or y≥2
minimum value is 2.
(B) (A+B)(A−B)=(A−B)(A+B)
⇒AB=BA
as A is symmetric and B is skew symmetric
⇒(AB)t=−AB
⇒k=1 and k=3
(C) a=log3log32⇒3−a=log23
Now 1<2−k+log32<2
⇒1<3.2−k<2
⇒log2(32)<k<log2(3)
⇒k=1 or k<2 and k<3
(D) sinθ=cosϕ⇒cos(π2−θ)=cosϕ
π2−θ=2nπ±ϕ
1π(θ±ϕ−π2)=−2n
⇒0 and 2 are possible.