Alan is 14 years old.This is twice as old as his brother James is.How old is James?
2 answers:
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Your calculator's cubic regression function can tell you the equation is
... f(x) = 2x³ + 5x² -12x = x(x +4)(2x-3)
The x-intercepts are -4, 0, +1.5.
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If you want to solve this "by hand", you can first of all recognize that since there is an x-intercept at 0, the cubic will only have three coefficients. That is, you can write the equation as
... f(x) = ax³ + bx² + cx
Substituting the given points (except (0, 0)) gives three linear equations in a, b, c.
... -a +b -c = 15 . . . . . for x=-1
... a + b + c = -5 . . . . for x=1
... 8a +4b +2c = 12 . . for x=2
adding the first two equations gives 2b=10, or b=5. Now, you can reduce the system to
... a + c = -10
... 4a +c = -4
Subtracting the first of these equations from the second gives 3a=6, or a=2. That tells you c=-12 (from a+c=10).
Then your equation is
... f(x) = x(2x² +5x -12)
Factoring by any of the usual techniques, or graphing, or using the quadratic formula will tell you the zeros (x-intercepts) are as above.
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Since the input values are sequential, you can also develop the function from differences of the output values. Those are 15, 0, -5, 12. First differences are -15, -5, +17. Second differences are +10, +22. The third difference is 12. Using the first of these differences in appropriate places in the interpolating polynomial formula, we have
... f(x) = 15 + (x+1)(-15 + (x)/2·(10 + (x-1)/3·(12))) = 2x³ +5x² -12x . . . . as above
A) The area of a rectangle is A = lw, where l=length of the rectangle and w=width of the rectangle. You know the length of the gift shop, l = 20x + 24. You know the width, w = 36x - 20. Plug those expressions into the equation for area of a rectangle and multiply/foil:
The expression for the area of the gift shop is
.
B) The equation for the perimeter of the gift shop is P = 2(l+w), where l = length and w = width. Plug your values for l and w into this equation:
The expression for the perimeter of the gift shop is 112x + 8
C) Since you know the perimeter is going to be 176 ft, that means P = 176. Plug that into the equation you found in part B, P = 112x + 8, and solve for x.
Once you solve for x, you can plug x into your equations for width and length to find the dimensions. x = 1.5, so:
1) L<span>ength = 20x+24 feet
</span>Length = 20(1.5) + 24 feet = 54 feet
2) Width = <span>36x-20 feet
Width = 36(1.5)-20 feet = 34 feet
Your dimensions are 54 feet (length) by 34 feet (width).</span>
The expression for the area of the gift shop is
B) The equation for the perimeter of the gift shop is P = 2(l+w), where l = length and w = width. Plug your values for l and w into this equation:
The expression for the perimeter of the gift shop is 112x + 8
C) Since you know the perimeter is going to be 176 ft, that means P = 176. Plug that into the equation you found in part B, P = 112x + 8, and solve for x.
Once you solve for x, you can plug x into your equations for width and length to find the dimensions. x = 1.5, so:
1) L<span>ength = 20x+24 feet
</span>Length = 20(1.5) + 24 feet = 54 feet
2) Width = <span>36x-20 feet
Width = 36(1.5)-20 feet = 34 feet
Your dimensions are 54 feet (length) by 34 feet (width).</span>