Question

Subtract:
(i) 5x from 2x
(ii) −xy from 6xy
(iii) 3a from 5b
(iv) −7x from 9y
(v) 10x² from −7x²
(vi) a² − b² from b² − a²

Answer 1

Change the sign of each term of the expression that is to be subtracted and then add.

(i) Term to be subtracted = 5x
Changing the sign of each term of the expression gives -5x.
On adding:

2x+(-5x) = 2x-5x
= (2-5)x
= -3x

(ii) Term to be subtracted = -xy
Changing the sign of each term of the expression gives xy.
On adding:

6xy+xy
= (6+1)xy
= 7xy

(iii) Term to be subtracted = 3a
Changing the sign of each term of the expression gives -3a.
On adding:

5b+(-3a)
= 5b-3a

(iv) Term to be subtracted = -7x
Changing the sign of each term of the expression gives 7x.
On adding:
9y+7x


(v) Term to be subtracted = 10x²
Changing the sign of each term of the expression gives -10x².
On adding:
−7x² + (-10x²) = −7x² −10x²
= (−7−10)x²
= −17x²

(vi) Term to be subtracted = a² − b²
Changing the sign of each term of the expression gives -a² + b².
On adding:
b² − a² + (-a² + b²) = b² − a² -a² + b²
= (1+1)b² +(−1-1) a²
= 2b² − 2a²