Question 25396
this is the hardest type of quadratic factorisation since you have to do some mental arithmetic!


we need 2 numbers that multiply to give 20...so 1x20 OR 2x10 OR 4x5
we need 2 numbers that multiply to give 10...so 1x10 OR 2x5

and we need the 4 numbers to combine to add up to 33!


And this is ignoring the signs --> we will think of those later.


So 1x20 is too big a gap...remember we want to get 33 ultimately. I think 4x5 is the best bet... so lets GUESS at (5y)(4y)


Now for the other 2...lets go for 2x5... 5*5 + 2*4 is 25+8 --> 33!!!


so, (5y-2)(4y-5)


I have added 2 negatives in, since -2x-5 is +10, yet we get -33 when we calcualte the 33 sum.


jon.