# Quadratic equation by factorisation (without using the standard formula)?

• Mar 31st 2010, 01:18 AM
Jay1001
Quadratic equation by factorisation (without using the standard formula)?
X2 -4x -165 = 0

must show that you have checked your answer by substituting the values obtained into the original expression

show each step of the solution,

Thanks
• Mar 31st 2010, 01:44 AM
watto23
The equation can be factorized by inspection. The two numbers in the brackets must multiply together to make -165, so.....

If you find all the prime factors of 165, they are 3, 5, and 11. and note that 3x5 = 15

You also know that the sum of the two numbers in the brackets must be -4.

and.....
11x-15=-165
11+(-15)=-4

x^2-4x-165 = (x+11)(x-15)
• Mar 31st 2010, 02:46 AM
Jay1001
(Nod)this may sound like a silly question but am new on here, what does this symbol represent (^), thanks for your help mate. is your answer to my question the fully solved answer??
• Mar 31st 2010, 02:51 AM
watto23
yer mate thats the answer. The ^ means 'to the power of'

so x^2 is x squared
and x^3 is x cubed etc.
• Mar 31st 2010, 02:59 AM
Jay1001
Cheers mate
• Mar 31st 2010, 03:03 AM
Jay1001
one more question mate, bit cheeky of me i know sorry.(Wink)
Solve the following quadratic equation by implementing the formula method.

Can you Show each step to the solution please.
5x2 + 5x – 4x2 + 2x= 20

The standard form of the quadratic equation is
Ax2 + bx + c = 0

How would this be solved??
• Mar 31st 2010, 05:09 AM
amul28
5x2 + 5x – 4x2 + 2x= 20
take x terms together n x^2 trems together
so u get

x^2+7x-20=0
u cannot factorise thie equation
if d equation is ax^2+bx+c=0
so use (-b+sq(b^2-4ac))/2a n (-b-sq(b^2-4ac))/2a
these two r the values of x
i guess u know this(Thinking)