Posted by Anonymous on Saturday, March 29, 2008 at 7:18pm.
Find the dot product of the following vectors:
a = (4, 1) b = (1,4)
a = (7,8) b = (4, 7)
You have to find the angle too.
Can someone please do these?

Math  Damon, Saturday, March 29, 2008 at 9:22pm
4*1 + 1*4 = 0
cos angle = 0, so angle is 90 or 90 (240)
remember algebra 1
y = m x + b
the slope of a line perpendicular to that is 1/m
here we have a slope of 1/4
and the other slope is 4/1
sure enough, perpendicular
7*4 + 8*7
7*(48)= 28
A*B* cos angle = 28
sqrt(49+64)*sqrt(16+49)* cos angle = 28
10.6 * 8.06 *cos angle = 28
cos angle = .328
angle = 109 deg