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Find the two values of y which satisfy the simultaneous equa...

Find the two values of y which satisfy the simultaneous equation 3x + y = 8, x2 + xy = 6.

A.

-1 and 5

B.

-5 and 1

C.

1 and 5

D.

1 and 1

Correct answer is A

3x+y=8...(i)

x2+xy=6...(ii)

From (i), y=83x

From (ii), xy=6x2y=6x2x

Equating the two values of y, we have

83x=6x2xx(83x)=6x2

8x3x2=6x26x28x+3x2=0

2x28x+6=0

x24x+3=0

x23xx+3=0x(x3)1(x3)=0

(x1)(x3)=0

y = 8 - 3x

When x = 1, y = 8 - 3(1) = 5

When x = 3, y = 8 - 3(3) = -1

\therefore \text{y = -1 or 5}