Question

method of substitution a+3b=5 and 7a-8b=6​

Answer 1

Answer :-

$\bf\huge\boxed{a = 2 ; b = 1}$

Solution :-

a + 3b = 5 ........(i)

7a - 8b = 6 .......(ii)

From equation (i), we get :-

=> a + 3b = 5

=> a = 5 - 3b .......(iii)

Substituting the value of a in eqn.(ii), we get :-

=> 7a - 8b = 6

=> 7(5 - 3b) - 8b = 6

=> 35 - 21b - 8b = 6

=> - 21b - 8b = 6 - 35

=> - 29b = -29

=> 29b = 29

=> b = 29/29

=> b = 1

Hence, the value of b is 1

Now,

Putting the value of b in eqn.(iii) :-

=> a = 5 - 3b

=> a = 5 - 3 × 1

=> a = 5 - 3

=> a = 2

Hence, the value of a is 2.

Answer 2

transpose 3 b to r.h.s

1. a=5-3 b
2. 7 a=6-8 b

substitute a value in equation 2

7(5-3 b) =6-8 b

35-21 b=6-8 b

-8 b+b=8

7 b=8

b=7/8

substitute b value in 1

a=5-3(7/8)

a=19/8