Giải phương trình vi phân sau
Y"=2y'+y=e^x

You likely mean to write the differential equation,

y'' - 2y' + y = exp(x)

The homogeneous part

y'' - 2y' + y = 0

has characteristic equation

r² - 2r + 1 = (r - 1)² = 0

with a root at r = 1 with multiplicity 2, so the characteristic solution is

y = C₁ exp(x) + C₂ x exp(x)

For the particular solution, we assume an ansatz

y = ax² exp(x)

where a is an unknown constant. Differentiating the ansatz twice:

y' = ax² exp(x) + 2ax exp(x) = (ax² + 2ax) exp(x)

y'' = (ax² + 2ax) exp(x) + (2ax + 2a) exp(x) = (ax² + 4ax + 2a) exp(x)

Substitute y and its derivatives into the DE:

(ax² + 4ax + 2a) exp(x) - 2 (ax² + 2ax) exp(x) + ax² exp(x) = exp(x)

Solve for a :

(ax² + 4ax + 2a) - 2 (ax² + 2ax) + ax² = 1

2a = 1

a = 1/2

Then the particular solution is

y = 1/2 x² exp(x)

The general solution is then

y = C₁ exp(x) + C₂ x exp(x) + 1/2 x² exp(x)

answer: the sun

explanation:

water cycle describes the evaporation of water from earth's surface, formation of clouds and precipitation water back onto the surface of earth. seventy percent of the earth is covered with water in the form of seas and oceans. the heat of the sun causes the evaporation of water from the surface of the ocean. the water vapors rise and condense to form water droplets. the collection of these water droplets form clouds which rain down again.

the evaporation of the oceans surface water as part of the water cycle is caused by the sun