fun f(x: Double): Double {
    return x * x + 2 * x
}
 
fun rectanglesMethod(a: Int, b: Int, n: Int): Double {
    val rectangleWidth = (b - a).toDouble() / n.toDouble()
    var area = 0.0
    var currentPoint = a.toDouble()
 
    for (i in 1..n) {
        currentPoint += rectangleWidth
        val rectangleHeight = f(currentPoint)
        area += rectangleHeight * rectangleWidth
    }
 
    return area
}
 
 
fun main() {
    val a = 0
    val b = 10
    val n = 100
 
    val area = rectanglesMethod(a, b, n)
 
    println(area)
}

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