Because the denominator->; 0, the limit value =6 is a constant.

So molecules must be->; 0, that is, 1-√2sina-2=0, sina=-√2/2.

Original limit = lim (x->; 1)(x^2+x-2)/(x+cosb)(x- 1)

= lim(x->； 1)(x+2)(x- 1)/(x+cosb)(x- 1)

= lim(x->； 1) (x+2)/(x+cosb)

=3/( 1+cosb)

=6

So cosb=- 1/2.

According to the meaning of the question, a=5π/4 and b=2π/3.