Find the values of y which satisfy the simultaneous equations x + y = 5, x2 – 2y2 = 1
- -12, -2
- -12, 12
-
-12, +2
- 2, -2
The correct answer is: C
Explanation
x + y = 5.......(i)
x2 - 2y2 = 1.......(ii)
x = 5 - y.........(iii)
Subst. for x in eqn.(ii) = (5 - y)2 - 2y2 = 1
25- 10y + y2 - 2y2 = 1
25 - 1 = y2 + 10y
y2 + 10y2 - 24 = 0
(y + 12)(y - 2) = 0
Then Either y + 12 = 0 or y - 2 = 0
= (-12, +2)