Question

Hi, the answer is K but can anyone show why

Answer 1

Let's do 51 and 52.

51. The contrapositive has the same truth value as the original statement. That's opposed to the converse, which may or may not be true independent of the original statement.

The contrapositive of IF P THEN Q is IF not Q THEN not P.  They're equivalent.  Here that's If the cat is not female then it is not tricolor.

Answer: C

52.  

$(x^3)^{(4-b^2)}=1$

$x^{3(4-b^2)} = 1$

For the statement to be true, the exponent must be zero:

$3(4-b^2) = 0$

$b^2 = 4$

$b = \pm 2$

Both positive 2 and negative 2 have a square of 4.

Answer: K

By the way, usually we assume $0^0=1$ so the restriction that $x \ne 0$ isn't really necessary.  Think of the definition of a polynomial or the binomial expansion:

$\displaystyle f(x)=\sum_{k=0}^n a_k x^k$

$\displaystyle(x+y)^n=\sum_{k=0}^n {n \choose k} x^{k}y^{n-k}$

For these common equalities to work when $x=0$ we need to define $0^0=1$