Q.7 Simplify these expressions and find their values if x = 3, a = -1, b = -2.
(i) 3x – 5 – x + 9
(ii) 2 – 8x + 4x + 4
(iii) 3a + 5 – 8a + 1
(iv) 10 – 3b – 4 – 55
(v) 2a – 2b – 4 – 5 + a

(i) 3x – 5 – x + 9 = 2x + 4
Putting x = 3, we get
2 × 3 + 4
= 6 + 4 = 10
(ii) 2 – 8x + 4x + 4
= -8x + 4x + 2 + 4
= -4x + 6
Putting x = 3, we have
= -4 × 3 + 6
= -12 + 6 =-6
(iii) 3a + 5 – 8a +1
= 3a – 8a + 5 + 1
= -5a + 6
Putting a = -1, we get
= -5(-1) + 6
= 5 + 6 = 11
(iv) 10 – 3b – 4 – 5b
= -3b – 5b + 10 – 4
= -8b + 6
Putting b = -2, we get
= -8(-2) + 6
= 16 + 6 = 22
(v) 2a – 2b – 4 – 5 + a
= 2a + a – 2b – 4 – 5
= 3a – 2b – 9
Putting a = -1 and b = -2, we get
= 3(-1) – 2(-2) – 9
= -3 + 4 – 9
= 1 – 9 = -8