Question x-k-x-

2.2 Nonlinear Equations in One Variable - Quadratic solving (factoring, quadratic formula, completing square)
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x k x - 56 = -16

In the given equation, k is an integer constant. If the equation has no real solution, what is the least possible value of k ?

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x k x - 56 = - 16 In the given equation, k is an integer

Hard-difficulty · SAT Math · Nonlinear Equations in One Variable — Quadratic solving (factoring, quadratic formula, completing square). Read the question above, select your answer, and check the full explanation below to understand exactly why the correct choice works.

Answer explanation

The correct answer is 50 . An equation of the form ax2+bx+c=0, where a , b , and c are constants, has no real solutions if and only if its discriminant, b2-4ac, is negative. Applying the distributive property to the left-hand side of the equation xkx-56=-16 yields kx2-56x=-16. Adding 16 to each side of this equation yields kx2-56x+16=0. Substituting k for a , -56 for b , and 16 for c in b2-4ac yields a discriminant of -562-4k16, or 3,136-64k. If the given equation has no real solution, it follows that the value of 3,136-64k must be negative. Therefore, 3,136-64k<0. Adding 64 k to both sides of this inequality yields 3,136<64k. Dividing both sides of this inequality by 64 yields 49<k, or k>49. Since it's given that k is an integer, the least possible value of k is 50