Why is 5 x -4 = -20 ?
Think of it as money. If I have four dollars then that's +4.
If I owe 4 that's -4. If 5 of us owe 4 that means 20 is owed = -20 dollars
a PLUS times a MINUS is a MINUS. Accept it.
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-18
x2 - x = 20 x2 - x - 20 = 0 (x - 5)(x + 4) = 0 x - 5 = 0 and x + 4 = 0 So, x = 5 ans x = -4
5x=4y=-20 x=-4 y=-5 (-4,-5) is the ordered pair
4x = 20 x = 5 (divide both sides by 4)
That's what the communtitive property is, changing the order. like 4+5=9; 5+4=9. So 4x5=20 and 5x4=20.