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## function1 – Function from points (challenge)

Write a program that given a pair of assignments
*f(x₁) = y₁* and *f(x₂) = y₂*,
calculates the function *f*, given by
*f(x) = ax + b*.

**Example 1.** If *f(0) = 2* and *f(2) = 3* then *f(x) = x/2 + 2*.

**Example 2.** If *f(1) = 6* and *f(4) = 12* then *f(x) = 2x + 4*.

### Input and output

The input contains a single line with 4 numbers
*x₁*, *y₁*, *x₂* and *y₂*

where *0 ≤ x₁, y₁, x₂, y₂ ≤ 100*

The output should contain a single line with a function description to the
standard output in the form `f(x) = A.A*x + B.B`

where `A.A`

and `B.B`

are the coefficients rounded to one decimal place.

Inputs are given so that it is always possible to produce such function.

#### Example input 1

```
0 2 2 3
```

#### Example output 1

```
f(x) = 0.5*x + 2.0
```

#### Example input 2

```
1 6 4 12
```

#### Example output 2

```
f(x) = 2.0*x + 4.0
```

### Scoring

- 2/60: works for the above examples but produces output in an incorrect format
- 4/60: works for the above examples and produces output in the correct format
- 60/60: produce output in the correct format with the correct coefficients

try first: pi

try next: function

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