If x+y=5,x-y=4,find the value of x²-y²

20

Step-by-step explanation:

→ First find the value of x and y

x + y = 5

x - y = 4

→ Add the equations to cancel out the y's

2x = 9

→ Divide both sides by 2 to find the value of x

x = 4.5

→ Substitute x = 4.5 back into x - y = 4 to find the value of y

4.5 - y = 4

→ Minus 4.5 from both sides to isolate -y

-y = -0.5

→ Multiply everything by -1

y = 0.5

→ Substitute x = 4.5 and y = 0.5 into x² - y²

4.5² - 0.5² = 20.25 - 0.25 = 20

step-by-step explanation: a reaction is first order. if the initial reactant concentration is 0.0200 m, and 25.0 days later the concentration is 6.25 x 10-4 m, then its half-life is:

my acc plz

step-by-step explanation: