Question

How many triangles can be formed by joining 9 points when 5 of them are collinear?
​

Answer 1

Step-by-step explanation:

The total number of ways to form a triangle by 9 points are given by,

9

C

3

but since 5 points are collinear no triangles can be formed using these points.

So,

9

C

3

−

5

C

3

=84−10=74

Answer 2

The total number of ways to form a triangle by 9 points are given by,

9

C

3

but since 5 points are collinear no triangles can be formed using these points.

So,

9

C

3

−

5

C

3

=84−10=74

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