Food versus Education The percentage y (of total personal consumption) an individual spends on food is approximately y = 35 x − 0.25 percentage points ( 6.5 ≤ x ≤ 17.5 ) , where x is the percentage the individual spends on education. An individual finds that she is spending x = 7 + 0.2 t percent of her personal consumption on education, where t is time in months since January 1. Use direct substitution to express the percentage y as a function of time t (do not simplify the expression), and then use the chain rule to estimate how fast the percentage she spends on food is changing on November 1. Be sure to specify the units. [ HINT: See Example 3(a).]
Food versus Education The percentage y (of total personal consumption) an individual spends on food is approximately y = 35 x − 0.25 percentage points ( 6.5 ≤ x ≤ 17.5 ) , where x is the percentage the individual spends on education. An individual finds that she is spending x = 7 + 0.2 t percent of her personal consumption on education, where t is time in months since January 1. Use direct substitution to express the percentage y as a function of time t (do not simplify the expression), and then use the chain rule to estimate how fast the percentage she spends on food is changing on November 1. Be sure to specify the units. [ HINT: See Example 3(a).]
Solution Summary: The author calculates the percentage y (of total personal consumption) an individual spends on food as a function of time t by using direct substitution.
Food versus Education The percentage y (of total personal consumption) an individual spends on food is approximately
y
=
35
x
−
0.25
percentage points
(
6.5
≤
x
≤
17.5
)
,
where x is the percentage the individual spends on education. An individual finds that she is spending
x
=
7
+
0.2
t
percent of her personal consumption on education, where t is time in months since January 1. Use direct substitution to express the percentage y as a function of time t (do not simplify the expression), and then use the chain rule to estimate how fast the percentage she spends on food is changing on November 1. Be sure to specify the units. [HINT: See Example 3(a).]
4. Use method of separation of variable to solve the following wave equation
მłu
J²u
subject to
u(0,t) =0, for t> 0,
u(л,t) = 0, for t> 0,
=
t> 0,
at²
ax²'
u(x, 0) = 0,
0.01 x,
ut(x, 0) =
Π
0.01 (π-x),
0
Solve the following heat equation by method of separation variables:
ди
=
at
subject to
u(0,t) =0, for
-16024
ძx2 •
t>0, 0 0,
ux (4,t) = 0, for
t> 0,
u(x, 0) =
(x-3,
\-1,
0 < x ≤2
2≤ x ≤ 4.
ex
5.
important aspects.
Graph f(x)=lnx. Be sure to make your graph big enough to easily read (use the space given.) Label all
6
33
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