Step-by-step explanation:
The upstream speed is S / t₁, and the downstream speed is S / t₂.
If we say f is the speed of the fish in calm water, and r is the speed of the river, then:
f − r = S / t₁
f + r = S / t₂
If we say T is the time it takes to cross the river, then the speed perpendicular to the river is ℓ/T, the speed parallel to the river is r, and the overall speed is f.
Using Pythagorean theorem:
f² = (ℓ/T)² + r²
f² − r² = (ℓ/T)²
(f − r) (f + r) = (ℓ/T)²
(S / t₁) (S / t₂) = (ℓ/T)²
S² / (t₁ t₂) = (ℓ/T)²
(t₁ t₂) / S² = (T/ℓ)²
√(t₁ t₂) / S = T/ℓ
T = ℓ√(t₁ t₂) / S
Numerators will be equal after the multiplication.
Counting each visible cube, and multiplying it by 2, he used 112. If you counted them, there would be 56 cubes. You'd multiply by 2 for the non-visible ones.
Answer:
C
Step-by-step explanation:
Use the pythagorean theorem
a² + b² = c²
3² + 4² = c²
9 + 16 = c²
25 = c²
5 = c
It has 4 equal sides, but it can be "squished" so all 4 angles are not equal