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Cubic, reciprocal, exponential and circle graphs

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課程筆記

Cubic graphs

  • A cubic has equation y = ax³ + bx² + cx + d with a ≠ 0. The simplest, y = x³, passes through the origin and has rotational symmetry.
  • A cubic with positive x3 rises from bottom-left to top-right; with negative x3 it falls. It can cross the x-axis up to three times.

Reciprocal graphs

  • For k ≠ 0, y = k/x is a hyperbola with two separate branches. It is undefined at x = 0.
  • It never touches the axes: the axes are asymptotes. x = 0 is undefined.
  • The graph is symmetrical about the lines y = x and y = -x.

Cubic and reciprocal curves

Cubic and reciprocal curvesO−6−4−2246−3−2−1123xyy = 1/xy = x³

Exponential graphs

  • y = ax (with a > 0, a \neq 1) grows or decays rapidly. y = 2x passes through (0, 1) because 20 = 1.
  • For a > 1 the graph rises ever more steeply; for 0 < a < 1 (e.g. y = (\frac{1}{2})x) it decays towards the x-axis, which is an asymptote.
  • Never negative: y > 0 for all x.

Exponential growth

Exponential growthO123456789−3−2−1123xyy = 2ˣ(0, 1)

Circle graphs

  • A circle with centre the origin and radius r has equation x2 + y2 = r2. For x2 + y2 = 25, the radius is 5.
  • To check if a point lies on the circle, substitute it: (3, 4) gives 9 + 16 = 25, so it does.
  • The tangent to a circle is perpendicular to the radius at the point of contact.

x² + y² = 25

x² + y² = 25r = 5 units

Recognising graphs

  • Link the shape to the equation: line, parabola, cubic S-shape, hyperbola, exponential curve, circle.

投影片

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練習題

免費預覽——35 題中的 8 題。註冊即可查看全部。
  1. 1.What is the shape of the graph of y = \frac{1}{x} called?

    Easy
    • Aparabola
    • Bhyperbola
    • Cellipse
    • Dcubic
  2. 2.What is y when x = 0 on y = 2x?

    Easy
    • A0
    • B1
    • C2
    • Dundefined
  3. 3.What is y when x = 3 on y = 2x?

    Easy
    • A6
    • B8
    • C9
    • D5
  4. 4.What is y when x = 2 on y = x3?

    Easy
    • A6
    • B8
    • C9
    • D5
  5. 5.What is y when x = -2 on y = x3?

    Easy
    • A8
    • B-8
    • C6
    • D-6
  6. 6.What is y when x = 4 on y = \frac{1}{x}?

    Easy
    • A4
    • B0.25
    • C0.4
    • D-4
  7. 7.What is y when x = -2 on y = \frac{6}{x}?

    Easy
    • A3
    • B-3
    • C12
    • D-12
  8. 8.Which value of x can't be used in y = \frac{1}{x}?

    Easy
    • A1
    • B0
    • C-1
    • D10

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