If 4 is one solution of the equation X^2 +3x +k =10, where k is constant, what is the other solution?
A)-7
B) -4
C) -3
D) 1
E)6
I took out the page that explains the answer. The answer is A. PLEASE explain
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Math - OG 38.
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life is a test
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try to factor the eqn to see the two solutions to the eqns. You know 4 is one solution hence one of the brackets will have (x-4) and you also know that 3x is part of the equation so you need another bracket which will multiply out to give 3x; only (x+7) will work since (x-4) (x+7) = x^2 + 3x... hence the other solution must be x=-7.odod wrote:If 4 is one solution of the equation X^2 +3x +k =10, where k is constant, what is the other solution?
A)-7
B) -4
C) -3
D) 1
E)6
I took out the page that explains the answer. The answer is A. PLEASE explain
hope that helps.
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papgust
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You could also substitue 4 in the equation as you already know that 4 is one solution.
You get k=-18. Sub k in eqn, you get this - x^2+3x-28=0.
Factorize and you will find that -7 is another solution.
You get k=-18. Sub k in eqn, you get this - x^2+3x-28=0.
Factorize and you will find that -7 is another solution.
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Scott@TargetTestPrep
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Solution:odod wrote:If 4 is one solution of the equation X^2 +3x +k =10, where k is constant, what is the other solution?
A)-7
B) -4
C) -3
D) 1
E)6
I took out the page that explains the answer. The answer is A. PLEASE explain
The phrase "4 is one solution of the equation" means that one value of x is 4. Thus, we first must plug 4 for x into the given equation to determine the value of k. So we have
4^2 + (3)(4) + k = 10
16 + 12 + k = 10
28 + k = 10
k = -18
Next we plug -18 into the given equation for k and then solve for x.
x^2 + 3x - 18 = 10
x^2 + 3x - 28 = 0
(x+7)(x-4) = 0
x = -7 or x = 4
Thus, -7 is the other solution.
The answer is A
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