No, absolutely Not
You can not cross out(Xy) 's when there is + sign there.
This business of crossing out is a big epidemic symptom among many student.
Think :
4 +^{ 1} the result is 2
1/4 = 9/2
2 4
If you cross out the 4 's , end up with 1 1 ,which is dead wrong.
2
Crossing out comes from simplifying a fraction.
16/12 = ( 2. 2. 2.2 ) / ( 2 .2. 3 ) = 4/3
Here we are crossing out two factors of 2 from numerator and denominator by dividing both of
them with the same common factor to simplifying our fractions to 4/3
Now if we have
16/ 5 * 7/ 12 Since multiplication of fractions implies multiplying numerator and denominators of
both fractions to get the numerator and denominator of the product , and
multiplication is Commutative( factors can change their position) , we can cross out factors of 4
from 16 and 12.
16/ 5 * 7/12 = 4/5 * 7/3 = 28/ 15
Keep in mind that Crossing out can only be done when there is common factor exists in
between numerator of one fraction and denominator of other, multiplying 2 or
more fractions together.
2.
to solve the quadratic
12X^2 + 7x = 10
12 X^2 + 7X  10 =0
Move everything to one side , let it equal 0 , and solve it either by factoring or using
quadratic formula.
3/29/2014

Parviz F.
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