Question 982866
Please limit to one question per post.
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1. the perimeter of a five sided figure with sides 2x-3 cm plus 2x-3 cm plus 12 cm plus 2x cm plus x square is 78 cm. what is the value of x?
2x-3cm+2x-3cm+12cm+2xcm+x^2=x^2+6x+6=78cm
x^2+6x+6=78cm
x^2+6x-72=0
(x-6)(x+12)=0
x-6=0 OR x+12=0
x=6cm OR x=-12cm
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2. No tables given to choose which.
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3. Which inequality is equivalent to -3x + 2y > 5y + 9? 
-3x-3y>9
x+y<-3
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4. solve the quadratic equation -4.5x squared + 72 = 0 
-4.5x^2+72=0 Multiply by -2
9x^2-144=0
(3x-12)(3x+12)=0
3x-12=0 OR 3x+12=0
3x=12 OR 3x=-12
x=4 OR x=-4
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5. if f(x) is 2/3x squared + 8x, what is the value of f(6)?
I got 56 which is the wrong answer. 
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It depends on the intent of the equation.  The problem is ambiguous.
Use parentheses to clarify:
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{{{f(x)=(2/3x)^2+8x}}} f(6)=48 and 1/81
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{{{f(x)=(2/3)x^2+8x}}} f(6)=72
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{{{f(x)=2/(3x^2)+8x}}} f(6)=48 and 1/54