Question

Solve x-y=21, 3x +y = 9 by
a substitution method​

Answer 1

Answer:

x-y=21. ......,..... equation 1

3x+y=9. ......,.... equation 2

from equation 1

We get,

x=21+y. ............ equation 3

substitute this value in equation 2

We get,

3(21+y)+y=9

63+y+y=9

63+2y=9

2y= 9-63

2y=-54

y= -54/2

y= -27

put y=-27 in equation 1

x-y=21

x-(-27)=21.

x+27=21

x=21-27

x=-6

therefore,(x,y) = (-6,-27)

I hope it's helpful

Answer 2

Answer :-

• Value of x = 39
• Value of y = 18

Given :-

• Two equations x - y = 21 and 3x + y = 9

To Find :-

• Values of x and y.

Solution :-

Here

• x - y = 21
• 3x + y = 9

Let

• x - y = 21 ...i)
• 3x + y = 9 ...ii)

Solve eq i)

⇒ x - y = 21

⇒ x - 21 = y

⇒ x = 21 + y ...iii)

Put the value of x in eq ii)

⇒ 3x + y = 9

⇒ 3 (21 + y) + y = 9

⇒ 63 + 3y + y = 9

⇒ 63 + 4y = 9

⇒ 4y = 63 + 9

⇒ 4y = 72

⇒ y = 72/4

⇒ y = 18

Put the value of y in eq i)

⇒ x - y = 21

⇒ x - 18 = 21

⇒ x = 21 + 18

⇒ x = 39

Hence, the value of x and y are 39 and 18 respectively.