Explain why n(n-1) must be an even number​

n & n - 1 are two consecutive numbers which means one of is surely even and the other one is odd.

Suppose that n is an even number;

So we can right n like this :

n = 2t

Thus :

n - 1 = 2t - 1

n( n - 1 ) = 2t( 2t - 1 ) = 2 ( 2t^2 - t )

= 2 ( q ) = 2q

The number obtained is a multiple of 2, so it is definitely even because all numbers are even multiples of 2.

(sin 42)/31. = sinx)/37

sinx = 37 (sin42)/31

= 37× 0.66/31 = 0.787

x= 51.9

other angle opposite to y = 180-51.9-42

= 180- 93.9 =86.1

so

sin42)/31 = sin 86.1)/y

0.021 = 0.997 /y

y= 0.997/0.021 =47.47