Using the "complete the square" method, solve the following x^2 +4x - 21 =0

x2+4x-21= 0,  This can be factorised into brackets as shown: (x+2)- 4 - 21 = 0 SImplified, so all x's are on one side of the equation: (x+2)= 25, Removing square root, DONT FORGET "±" : (x+2) = ± 5,  Solve for two solutions: x = 3, x = -7

CS
Answered by Charlotte S. Maths tutor

5457 Views

See similar Maths A Level tutors

Related Maths A Level answers

All answers ▸

What's the deal with Integration by Parts?


y=e^2x-11e^x+24 Find the stationary point, nature of the stationary point, the x-intercepts and the y-intercept (calculator allowed)


Figure 1 shows a sector AOB of a circle with centre O and radius r cm. The angle AOB is θ radians. The area of the sector AOB is 11 cm2 Given that the perimeter of the sector is 4 times the length of the arc AB, find the exact value of r.


The quadratic equation (k+1)x^2+12x+(k-4)=0 has real roots. (a) Show that k^2-3k-40<=0. (b) Hence find the possible values of k.


We're here to help

contact us iconContact ustelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo

MyTutor is part of the IXL family of brands:

© 2025 by IXL Learning