Factorise and solve X^2+8X+15=0
For any equation in the form ax^2+bx+c and a=1, the first step is to find a set of numbers. In this case, they must add up to 8 (b) and multiply to 15 (c).
With trial and error, it can be found that these are +3 and +5.
Thus, factorise the equation to get (X+3)(X+5)=0.
We know from this that X+3=0 or X+5=0.
Hence, we can solve both equations to get X=-3 and X=-5.
JA
Related Maths GCSE answers
All answers ▸A house is bought for £150,000 at the start of 2005. For 3 years it loses 10% of its original value per year. After this time it loses 10% per year. What was its value at the end of 2011/start of 2012?
Solve 5x^2 = 10x + 4 , to 2 decimal places.
Solve the following simultaneous equations: (1) 4x+y=7 and (2) 3x+2y=9
Factorise the following equation: y = 2x^2 + 4x - 6