Asked by dennyelle
y = ax^2+ bx + 9 has x-intercepts at x = -3 and x = 1.
what is the value of a?
what is the value of b?
please help!!
what is the value of a?
what is the value of b?
please help!!
Answers
Answered by
oobleck
knowing the roots, you know that
a(x+3)(x-1) = ax^2+bx+9
a(x^2+2x-3) = ax^2+bx+9
2a = b
-3a = 9
a(x+3)(x-1) = ax^2+bx+9
a(x^2+2x-3) = ax^2+bx+9
2a = b
-3a = 9
Answered by
mathhelper
alternate way:
f(x) = ax^2 + bx + 9
f(-3) = 9a - 3b + 9 = 0 , 3a - b = -3
f(1) = a + b = -9
add, 4a = -12
a = -3, mentally get b = -6
f(x) = ax^2 + bx + 9
f(-3) = 9a - 3b + 9 = 0 , 3a - b = -3
f(1) = a + b = -9
add, 4a = -12
a = -3, mentally get b = -6
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