CMA Foundation · Fundamentals of Business Mathematics and Statistics · Quadratic Equations
What are the roots of the equation x^2 - 9x + 20 = 0?
The roots are 4 and 5. The equation factorises as (x-4)(x-5)=0 because 4 and 5 add up to 9 and multiply to 20, so each bracket set to zero gives one root of the quadratic.
- Ax = 4 and x = 5Correct
- Bx = -4 and x = -5
- Cx = 2 and x = 10
- Dx = 1 and x = 20
Explanation
Find two numbers with sum 9 and product 20: 4 and 5. So (x-4)(x-5)=0 gives x=4 or 5. Option -4 and -5 would give sum -9, which has the wrong sign.
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