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7.5 xxx. 8.0 xxx 8.5 xxx 9.0 xxxxx 9.5 xxxx
Answer:
x ≈ - 10.65, x ≈ - 5.35
Step-by-step explanation:
Given
(x + 8)² - 7 = 0 ( add 7 to both sides )
(x + 8)² = 7 ( take the square root of both sides )
x + 8 = ±
( subtract 8 from both sides )
x = - 8 ±
, thus
x = - 8 -
≈ - 10.65
x = - 8 +
≈ - 5.35
Answer:
6 knots
Step-by-step explanation:
Let the speed be v knots
then time taken to cover 500 M = 500 / v hrs
fuel consumption /hr = 216 + 0.5v^3
let F be the fuel consumption for trip
= [500/v][216 + 0.5v^3]
= 500[216/v + 0.5v^2]
dF/dv = 500[ - 216/v^2 + v]
d^2F/d^2v = 500[432/v^3 + 1] , i.e. +ve
so setting dF/dv will give a minima
500[ -216/v^2 + v] = 0
or v = 216/v^2
or v^3 = 216
solving, we get v = [216]^(1/3) = 6 knots