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Consider the relationship 7r+4t=14.a. Write the relationship as a function r=f(t).b. Evaluate f(−7).c. Solve f(t)=18.

Sagot :

We are given the relationship:

[tex]7r+4t=14[/tex]

a. It's required to find a relationship where r is a function of t. To do that, we need to solve the equation for r.

Subtract 4t:

[tex]7r=14-4t[/tex]

Divide by 7:

[tex]r=\frac{14-4t}{7}[/tex]

b. We use the function found in part a and evaluate it for t=-7:

[tex]\begin{gathered} r=\frac{14-4\cdot(-7)}{7} \\ \text{Operating:} \\ r=\frac{14+28}{7}=\frac{42}{7}=6 \end{gathered}[/tex]

Thus, f(-7) = 6

c. Solve f(t) = 18

Again, we use the function from part a and solve the equation:

[tex]\frac{14-4t}{7}=18[/tex]

Multiplying by 7:

[tex]\begin{gathered} 14-4t=7\cdot18 \\ 14-4t=126 \end{gathered}[/tex]

Subtract 14 and then divide by -4:

[tex]\begin{gathered} -4t=126-14 \\ -4t=112 \\ t=\frac{112}{-4}=-28 \end{gathered}[/tex]

t = -28