Answer:
14.3 km/h to 3 significant figures
Step-by-step explanation:
Let time travelling upstream be t1 hours and downstream = t2 hours.
t1 + t2 = 1.75..........................(1)
Let v be the speed of the boat in still water.
12 / t1 = v - 3.........................(2)
12 / t2 = v + 3........................(3)
From (1) and (3) , substituting for t2:-
12 / (1.75 - t1) = v + 3 ..................(4)
Subtract:- (2) - (4):-
12 / t1 - 12 / (1.75 - t1) = -6
12(1 .75 - t1) - 12t1 = -6t1(1.75 - t1)
21 - 12t1 - 12t1 = -10.5t1 + 6t^2
6t1^2 + 13.5t1 - 21 = 0
Solving this gives t1 = 1.058 hours
Therefore the speed in still water (v) = 12/1.058 + 3 = 14.3 to 3 sig figs
Answer:
B
Step-by-step explanation:
Given a quadratic equation in standard form
ax² + bx + c = 0 ( a ≠ 0 )
Then the discriminant is
Δ = b² - 4ac
• If b² - 4ac > 0 then 2 real irrational roots
• If b² - 4ac > 0 and a perfect square then 2 real rational roots
• If b² - 4ac = 0 then 1 real double root
• If b² - 4ac < 0 then 2 complex roots
Given
x² + 3x - 7 = 0 ← in standard form
with a = 1, b = 3, c = - 7 , then
b² - 4ac
= 3² - (4 × 1 × - 7) = 9 + 28 = 37
Since b² - 4ac > 0 then 2 real irrational roots
Answer:
I can't read this language
Step-by-step explanation:
