### Linear Interpolation In Excel

There are many ways to perform linear interpolation (or extrapolation) in Excel.
The examples below assume that you know at least two points (x1,y1) and (x2,y2) and want to solve for y given x based on the equation for a line: y=mx+b, where m is the slope and b is the y-intercept.

1. Using the Point-Slope formula, where the slope is (y2-y1)/(x2-x1):
```y=y1+(x-x1)*(y2-y1)/(x2-x1)
=B2+(B5-A2)*(B3-B2)/(A3-A2)```

2. Using the SLOPE and INTERCEPT functions to solve for m and b:
```y=SLOPE(y's,x's)*x+INTERCEPT(y's,x's)
=SLOPE(B2:B3,A2:A3)*B5+INTERCEPT(B2:B3,A2:A3)```

3. The TREND function uses linear regression to solve for y if you have two or more points. This is also a way to estimate y from a linear fit of many points.
```y=TREND(y's,x's,x,TRUE)
=TREND(B2:B3,A2:A3,B5,TRUE)```