Three pairs
When a line crosses two parallel lines:
- Alternate angles (a Z shape) are equal.
- Corresponding angles (an F shape) are equal.
- Co-interior angles (a C or U shape) add up to 180°.
Here a and 70° are alternate, so a = 70°.
Say why
On a paper, "give a reason" means name the fact: "alternate angles are equal", not "Z angles". Each step of a calculation needs its own reason.
Move the lines
In the graphing calculator, plot y = 2 and y = 5 (parallel) and y = 2x. Estimate the angles where y = 2x crosses each line: which pairs are equal?