Question

if there are 7 distinct points on a plane,What is the number of straight lines joining these points

Answer 1

Answer:

1 straight line passes through these points

Answer 2

The minimum number of  straight lines joining these points = 21.

Step-by-step explanation:

We know that , we need at-least one line to join two points.

i.e. The minimum number of points required to  join by a line = 2

The given number of points = 7

Using combination : $^nC_r=\dfrac{n!}{r!(n-r)!}$

The minimum number of  straight lines joining these points = $^7C_2$

$=\dfrac{7!}{2!(7-2)!}=\dfrac{7\times6\times5!}{2!5!}=21$

Hence, the minimum number of  straight lines joining these points = 21.

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