if x^2 + 9x + 20 = 0, what are the possible values of x?

So x2 + 9x + 20 = 0 My preffered way of solving this equation is to factorise the equation. (Though I understand that different students may find other ways easier) Factorisation is where the above equation is (x+a)(x+b) = 0 So if we times out (x+a)(x+b) we getx2 + ax + bx + ab = 0 therefore x2 + (a+b)x + ab = 0Therefore we can equate this to the original question, so x2 + 9x + 20 = x2 + (a+b)x + abso now we can see that 9 = a + b and 20 = abI would reccomend using trial and error (although I understand that different students may prefer other techniques).So by trying for multiple values of a and b, we can see that they must equal 5 and 4. Therefore x2 + 9x + 20 = (x+5)(x+4) = 0 We know that the only way of producing a 0 through multiplication is through multiplying one number by another. Therefore we know thatx+5= 0 or x+4=0 Through rearranging these equations we can conclude that x must equal -4 or -5. 

Answered by Tilly P. Maths tutor

7799 Views

See similar Maths GCSE tutors

Related Maths GCSE answers

All answers ▸

f(x) = 3x - 2a || g(x) = 2ax + 1 || fg(x) = 2x + b/2


Solve the quadratic 2x^2+7x+6 by completing the square


I struggle with long worded questions


Show that 12 cos 30° -2 tan 60° can be written in the form square root k where k is an integer.


We're here to help

contact us iconContact usWhatsapp logoMessage us on Whatsapptelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo
Cookie Preferences