Please explain how to do this

Option 4

Step-by-step explanation:

Area of a circle (A) = πr²(i)

Circumference (C) = 2πr

=>C = 2πr

=> 2πr= C

=> π = C/2r

Substituting the value of π = C/2r in the first equation i.e (i)

A = (C×r²)/2r

= (C . r)/2

= 1/2 × C × r

Therefore, option 4 is the correct option

the solution of the equation is 2.23 ⇒ answer b

step-by-step explanation:

* lets revise the meaning of exponential function

- the form of the exponential function is y = ab^x, where a ≠ 0, b > 0 ,  

  b ≠ 1, and x is any real number

- it has a constant base b

- it has a variable exponent x

- to solve an exponential equation, take the log or ln of both sides,  

  and solve for the variable

* lets solve the problem

∵

- the base is 7 and the exponent is x

- insert ㏑ in both sides

∴

- use the rule

∴ x ㏑(7) = ㏑(77)

- to find x divide both sides by ㏑(7)

∴

* the solution of the equation is 2.23 to the nearest 2 decimal places