Solution:
Let (1,8)=(x1,y1)
(-1,-2)=(x2,y2)
D=?
Now,
D=
[tex] \sqrt{(x2 - x1) ^{2} + (y2 - y1)} ^{2} [/tex]
or, D=
[tex] \sqrt{( -1 - 1) ^{2} + ( - 2 - 8) ^{2} } [/tex]
[tex] \sqrt{( -2) ^{2} + ( - 10) ^{2} } [/tex]
[tex] \sqrt{4 + 100 } [/tex]
[tex] \sqrt{104} [/tex]
2[tex] \sqrt{26} [/tex]
