Решение

fun checkStraightLine(coordinates: Array<IntArray>): Boolean {
    val dx = coordinates[1][0] - coordinates[0][0]
    val dy = coordinates[1][1] - coordinates[0][1]

    for (i in 2 until coordinates.size) {
        val x = coordinates[i][0] - coordinates[0][0]
        val y = coordinates[i][1] - coordinates[0][1]
        if (dx * y != dy * x) return false
    }
    return true
}