Steply

Graph x = t, y = t^2 - 3

Step by step, with the reason for every step · Parametric equations · Precalculus

Step by step

The question

Question: graph and remove t from x = t, y = t² − 3.

x = t and y = t2 − 3

1 Make a table

Each t gives a point.

Start with t = −2.

x is (−2): −2.

t = −2: x = (−2) = −2

y is (−2)² − 3: 1.

Minus times minus is plus.

y = (−2)² − 3 = 1

Put the t's in a table.

Work out x for each t,

−2
−1
0
1
2

and y for each t.

1
−2
−3
−2
1

2 Plot the points

Draw the grid.

Put each (x, y) on the grid.

3 Join in order of t

Join the points in order: t = −2, then −1, and on.

The arrows show the way t grows.

t can go on, so the curve goes on.

4 Remove t

So t = x.

t = x

Put t into y = t² − 3, with its bracket: y = (x)² − 3.

y = (x)2 − 3

Careful!

The whole of x is squared, not only the last number.

So it keeps its bracket.

Careful: not y = x² − 3 ✗

5 Check

Let's check with a point from the table: t = 2 gave (2, 1).

Put x = 2 into the answer.

We get y = 1, the same as the table.

Right!

x = 2: y = (2)² − 3 = 1

Let's look back.

First: make a table.

Then: plot the points.

Then: join in order of t.

Then: remove t.

Last: check.

Answer
Careful: not y = x² − 3 ✗

Your turn

Try this one yourself, then check:

Graph and remove t from x = t, y = t² − 4
Show the answer
y = (x)2 − 4

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