Ms. Math Teacher's CyberClassroom: MYP Algebra 2

Monday, October 06, 2008

Guided Practice
p.418 #3 and 4
Explain what is wrong with the composition shown.

Bear said...: For #3, they didn't substitute the 3x for the x2 in f(x)

#4 they 3x instead of x2+2. then they should have substituted in the 3x for the x2.; 6:04 PM
Anonymous said...: Adam

Error Analysis:
f(X) = X^2 +2 and g(X) = 3X
3. f(g(x)) = f(X^2 + 2)
= 3(X^2 + 2)
= 3X^2 + 6

-The problem here is that they substituted f(X) instead of f(g(X)), like they needed to.

4. f(g(x)) = f(3X)
= 3X^2 + 2

-The problem here is that they didn't replace the X in f(X) = X^2 + 2, which is what they needed to do, because f(3X) = X^2 + 2. The equation should look like this -> f(3X) -> (3X)^2 + 2 -> 9X^2 + 2; 6:36 PM
Anonymous said...: Page 418 #3,4

3) The mistake is that f(x) was inserted in the place of g(x). When g(x) and f(x) are inserted in the equation, it would be (3x)squared + 2. The solution would be (9x)^2 +2.

4) The mistake in this problem is that when (3x) is squared, the square is only distributed to the x, not the 3. THe final answer should be (9x)^2 + 2.; 9:36 PM
Anonymous said...: 3. The first step is wrong. It should be:
- f(3x)
- x^2(3x)+2
- 3x^3+2

They substituted g(x) into the expression incorrectly. G(x)=3x, not x^2+2. F was also substituted in incorrectly: it should be written as x^2(3x)+2 in that step.

4. In this composition, the first step is right, but f was substituted incorrectly into the expression. Instead of the first term being 3x^2, it should be 3x^3.; 9:38 PM

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