Math
posted by Sally .
Null factor law and factoriising:
2x^2+7x=0
X(2x+7)=0
X=0 or 2x+7=0. ( the answer in the book was x=7/2, how?
And. X^24=2x4
Is it x^242x+4=o ??? If so!' how do I continue?

2x^2+7x=0
X(2x+7)=0
X=0 or 2x+7=0
ok so far
Now, if the product of two numbers (A)(B) = 0
that can only be true of one of the, or both , are equal to zero.
(try multiplying any two numbers to get a result of 0)
so either x=0 or 2x+7 = 0
x = 0 says it all
in
2x+7 = 0
2x = 7 , (simple equation rule)
x = 7/2 , (simple equation rule)
your second question:
x^2  2x = 0 , after you take everything to the left
x(x2) = 0
same as above and even simpler. 
2 x ^ 2 + 7 x = 0
x ( 2 x + 7 ) = 0
Obviously solution x = 0
2 x + 7 = 0 Subtract 7 to both sides
2 x + 7  7 = 0  7
2 x =  7 Divide both sides by 2
x =  7 / 2
Solutions x = 0 and x =  7 / 2
x ^ 2  4 = 2 x  4 Add 4 to both sides
x ^ 2  4 + 4 = 2 x  4 + 4
x ^ 2 = 2 x Subtract 2 x to both sides
x ^ 2  2 x = 2 x  2 x
x ^ 2  2 x = 0
x ( x  2 ) = 0
Obviously solution x = 0
x  2 = 0 Add 2 to both sides
x  2 + 2 = 0 + 2
x = 2
Solutions x = 0 and x = 2