Problem: A straight line joins the points (−1,1)(-1,1)(−1,1) and (3,9)(3,9)(3,9). Its xxx-intercept is:
Answer Choices:
A. −3/2-3 / 2−3/2
B. −2/3-2 / 3−2/3
C. 2/52 / 52/5
D. 222
E. 333 Solution:
y=mx+by=m x+by=mx+b is satisfied by (−1,1)(-1,1)(−1,1) and (3,9)(3,9)(3,9)
1=−m+bm=29=3m+bb=3y=2x+2x+3\left.\begin{array}{rlr} 1 & =-m+b & & m=2 \\ 9 & =3 m+b & & b=3 \end{array}\right. \qquad y=2 x+2 x+3 19​=−m+b=3m+b​​m=2b=3​y=2x+2x+3
when y=0,x=−3/2y=0, x=-3 / 2y=0,x=−3/2