Question

Multiply mentally and write only the products for each of the following:-
i) (3-x) (5-x)​

Answer 1

Answer:

=3×5- (3 into x) -(x into 5)- (x into -x)

= 15-3x-5x-(-x square)

=15-8x+x square | { -×-=+}|

||ANOTHER METHOD||

using identity- (x+a)(x+b)=x square + (a+b)x+ab

=(3-x)(5-x)

= {(-x)+3} {(-x)+5}

=(-x) square+(3+5)(-×)+(3×5)

= x square +8(-x)+15

= x square -8x+15 or u can write it as

15-8x+x