I need help please I dont understand ​

u can use formula whole root ,( x2-x1)²+(y2-y1)²

hope it helps...

7.8 (1.d.p) or √61

Step-by-step explanation:

To solve this question we must use Pythagoras (a²+b²=c²)

Imagine that the line given is the hypotenuse (the longest side of a right-angled triangle) of a right-angled triangle and the other sides as a line from B going to the right, and a line from A going downwards (making the final vertexes for the triangle at coordinates: (3,2), which is B,  (9,7), which is A, (9,2), which is the vertex the 2 imaginary lines we added, created) So now we use Pythagoras to find the length of the hypotenuse:

9-3=6 (subtracting the xs of vertexes A and B to find the length of the imaginary line we extended from B) and

7-2=5 (subtracting the ys of vertexes A and B to find the length of the imaginary line we extended from A)

Now to put them into Pythagoras's formula:

6²+5²=c² ⇒ 36+25=c² ⇒ √36+25=c ⇒ √61 = c ⇒ c = 7.8102

Which can be rounded to 7.8 (as the third digit, the 1, rounds down.