Um aparelho elétrico tem potência de 6500 watts. É usado quatro vezes ao dia. Sendo o valor do kwhR$0,25 determine o custo de energia elétrica no final de trinta dias, sabendo que o mesmo cada vez que é ligado no dia permanece ligado 2 horas e 36 minutos

After thirty days with the mentioned use the cost of the device is R$ 507,00.

Step-by-step explanation:

We first need to calculate its total power consumption over the 30 days. Since its turned on four times a day for 2 h and 36 min each, we need to multiply this time by 4 to have the time it's turned on in a day and multiply that by 30 to calculate its total power consumption. Although, we need to convert the time from hours and minutes to only hours, to do that we divide the minutes part by 60 and sum it on the hour part. All of this is done below:

After thirty days with the mentioned use the cost of the device is R$ 507,00.

the surface area is 124cm²

step-by-step explanation:

length: 4cm

width: 9cm

height:   2cm

the value of x is 9 ⇒ answer b

step-by-step explanation:

* we can solve this problem using cosine and sine rule

- in δ abc

∵ ab = 36 , bc = 28 , ac = 16

- lets find the measure of angle b using the cosine rule

∵ cos b = [ab² + bc² - ac²]/2(ab)(bc)

∴ cos b = [36² + 28² - 16²]/2(36)(28)

∴ cos b = 19/21

∴ m∠b = cos^-1(19/21) ≅ 25°

- lets find the measure of angle a using the sine rule

∵ sina/bc = sinb/ac = sinc/ab

∴ sina/28 = sin25°/16 ⇒ by using cross multiplication

∴ sina = 28 × sin25°/16

∴ sina = 0.7396

∴ m∠a = sin^-1(0.7396) ≅ 48°

- from the figure m∠abd = m∠dbc

∵ m∠abc = 25°

∴ m∠abd = 25°/2 = 12.5°

- in δabd

∵ m∠a = 48° , m∠abd = 12.5°

∵ the sum of the measures of the interior angles of any δ is 180°

∴ m∠adb = 180° - (48° + 12.5°) = 119.5°

∵ ab = 36

∵ ad = x

- use the sine rule to find x

∵ sin∠adb/ab = sin∠abd/x

∴ sin119.5°/36 = sin12.5°/x ⇒ by using cross multiplication

∴ x = 36 × sin12.5°/sin119.5° = 8.95 ≅ 9

* the value of x is 9