How to use the quadratic function - ACT Math

Card 0 of 4

Question

How many solutions are there to: x2 – 9 = 0

Answer

There are two solutions that make the solution true: 3 and **–**3.

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Question

Two consecutive negative odd numbers have a product of 15. What is the sum of the two numbers?

Answer

Define the variables x = first number and x + 2 = second number

The product is x(x + 2) = 15, so we need to solve the quadratic equation x2 + 2x – 15 = 0. Factoring we get (x + 5)(x – 3) = 0, so x = –5 or x = 3. The problem calls for negative numbers, so the answers are –5 and –3 and the sum is –8

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Question

What is the difference of the values of x that satisfy

4_x_2+ 3_x_ – 1 = 0?

Answer

Factor the equation (4_x_ – 1) (x + 1)

The solutions are x = –1 and x = 1/4.

The difference is (1/4) – (–1) = 5/4

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Question

2_x_ + y = 1

What is the slope and the y-intercept of the given equation, respectively?

Answer

You put the equation into slope-intercept form (y = mx + b)

The new equation is y= –2_x_ + 1

m = –2 and b = 1

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