Answer:
y = 54/25 when x = 4.
Step-by-step explanation:
y is given by the equation:
[tex]\displaystyle y = p\times q^{x-1}[/tex]
Where p and q are numbers.
We are also given that when x = 1, y = 10 and when x = 6, y = 0.7776.
And we want to determine the value of y when x = 4.
Since y = 10 when x = 1:
[tex]\displaystyle (10) = p\times q^{(1)-1}[/tex]
Simplify:
[tex]10 = p \times q^0[/tex]
Any number (except for zero) to the zeroth power is one. Hence:
[tex]p=10[/tex]
Thus, our equation is now:
[tex]y = 10\times q^{x-1}[/tex]
When x = 6, y = 0.7776. Thus:
[tex](0.7776) = 10\times q^{(6)-1}[/tex]
Simplify and divide both sides by ten:
[tex]\displaystyle 0.07776 = q^5[/tex]
Take the fifth root of both sides:
[tex]\displaystyle q = \sqrt[5]{0.07776}[/tex]
Use a calculator. Hence:
[tex]\displaystyle q = \frac{3}{5} = 0.6[/tex]
Our completed equation is:
[tex]\displaystyle y = 10\times \left(\frac{3}{5}\right)^{x-1}[/tex]
Then when x = 4, y equals:
[tex]\displaystyle \begin{aligned} y &= 10\times \left(\frac{3}{5}\right)^{(4)-1} \\ \\ &= 10\times \left(\frac{3}{5}\right)^3 \\ \\ &= 10\times \left(\frac{27}{125}\right) \\ \\ &= \frac{54}{25}\end{aligned}[/tex]
