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8. (a) Sketch the graph of $y = 7^x$, $x \\in \\mathbb{R}$, showing the coordinates of any points at which the graph crosses the axes - Edexcel - A-Level Maths: Pure - Question 10 - 2011 - Paper 3

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8.-(a)-Sketch-the-graph-of-$y-=-7^x$,-$x-\\in-\\mathbb{R}$,-showing-the-coordinates-of-any-points-at-which-the-graph-crosses-the-axes-Edexcel-A-Level Maths: Pure-Question 10-2011-Paper 3.png

8. (a) Sketch the graph of $y = 7^x$, $x \\in \\mathbb{R}$, showing the coordinates of any points at which the graph crosses the axes. (b) Solve the equation $$7^x... show full transcript

Worked Solution & Example Answer:8. (a) Sketch the graph of $y = 7^x$, $x \\in \\mathbb{R}$, showing the coordinates of any points at which the graph crosses the axes - Edexcel - A-Level Maths: Pure - Question 10 - 2011 - Paper 3

Step 1

Sketch the graph of $y = 7^x$

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Answer

To sketch the graph of the function y=7xy = 7^x, we start by identifying key points:

  1. Intercepts:

    • The graph intersects the y-axis at the point (0, 1) since 70=17^0 = 1.
    • The graph does not cross the x-axis since y=7x>0y = 7^x > 0 for all real x.
  2. Behavior:

    • As xoinftyx o -\\infty, y=7xy = 7^x approaches 0, and as xo+inftyx o +\\infty, yy increases without bound.
  3. Sketch:

    • Draw a smooth curve starting from the vicinity of (0, 1), approaching the x-axis from above as it moves left, and rising steeply as it moves right.

Step 2

Solve the equation $7^x - 4(7) + 3 = 0$

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Answer

To solve the equation, start by simplifying it:

7x28+3=07^x - 28 + 3 = 0 7x25=07^x - 25 = 0

This gives: 7x=257^x = 25 Taking the logarithm on both sides: x=log7(25)x = \log_7(25) Using the change of base formula: x=log(25)log(7)x = \frac{\log(25)}{\log(7)} Using a calculator to find the logarithm values: log(25)1.39794,log(7)0.84510\log(25) \approx 1.39794, \quad \log(7) \approx 0.84510 Then: x1.397940.845101.65x \approx \frac{1.39794}{0.84510} \approx 1.65

Therefore, the solution to two decimal places is: x1.65x \approx 1.65.

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