Find the area of triangle oab with o (0,0) a (4,0) and b (0,6).

Use the distance formula to find 2 sides. O through A and O through B.
distance formula is in the image.
OA
root[(x2-x1)^2+(y2-y1)^2]
root[(4-0)^2+(0-0)^2]
root[16]
4
OB
root[(x2-x1)^2+(y2-y1)^2]
root[(0-6)^2+(6-0)^2]
root[36+36]
root[72]
6root[2]
multiply the two numbers and divide by 2.
4 * 6root[2]
24root[2]
24root[2]/2
12root[2]