Question

26. Find the value of (5a - b) (3a - 2b) (4a - 3b) for a=1,b=2.
​

Answer 1

Step-by-step explanation:

a:b=2:5⇒

b

a

=

5

2

(3a+4b):(5a+6b)=

5a+6b

3a+4b

=

b

5a+6b

b

3a+4b

(On dividing both numerator and denominator by b)

b

5a

+6

b

3a

+4

=

5×

5

2

+6

3×

5

2

+4

=

2+6

5

6

+4

=

5

26

×

8

1

=

20

13

Answer 2

(5a - b) (3a - 2b) (4a - 3b)
If a = 1, b = 2

Let us first simply the given equation..

= [5a (3a - 2b) - b (3a - 2b)] (4a - 3b)
= (15a² - 10ab - 3ab + 2b²) (4a - 3b)
= (15a² - 13ab + 2b²) (4a - 3b)
= 4a(15a² - 13ab + 2b²) - 3b(15a² - 13ab + 2b²)
= 60a³ - 52a²b + 8ab² - 45a²b + 39ab² - 6b³
= 60a³ - 52a²b - 45a²b + 8ab² + 39ab² - 6b³
= 60a³ - 97a²b + 47ab² - 6b³

Now substituting the value of a and b in the above equation..

= 60(1)³ - 97(1)²(2) + 47(1)(2)² - 6(2)³
= 60 - 194 + 188 - 48
= 248 - 242
= 6

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