#include <bits/stdc++.h>
#define int long long
using namespace std;

const int N = 4e5 + 5;

int n, q, tot;
int c[N], head[N], ver[N], edge[N], nxt[N], dep[N];
int dp[N][21], f[N][21], cost[N][21];

void add(int x, int y, int z) {
	ver[++tot] = y, edge[tot] = z, nxt[tot] = head[x], head[x] = tot;
}

void dfs1(int x, int fa) {
	dep[x] = dep[fa] + 1, f[x][0] = fa;
	for (int i = head[x]; i; i = nxt[i]) {
		int y = ver[i], z = edge[i];
		if (y == fa) continue;
		dfs1(y, x);
		cost[y][0] = z, dp[x][0] = max(dp[x][0], dp[y][0] - 2 * z);
	}
}

void bfs() {
	queue<int> q; q.push(1);
	while (!q.empty()) {
		int x = q.front(); q.pop();
		for (int i = head[x]; i; i = nxt[i]) {
			int y = ver[i], z = edge[i];
			if (y == f[x][0]) continue;
			dp[y][0] = max(dp[y][0], dp[x][0] - 2 * z);
			q.push(y);
		}
	}
}

void init() {
	dfs1(1, 1); bfs();
	for (int j = 1; j <= 20; j++)
		for (int i = 1; i <= n; i++) {
			f[i][j] = f[f[i][j - 1]][j - 1];
			cost[i][j] = cost[i][j - 1] + cost[f[i][j - 1]][j - 1];
			dp[i][j] = max(dp[i][j - 1], dp[f[i][j - 1]][j - 1]);
		}
}

int lca(int x, int y) {
	int ans = c[x] + c[y], mx = max(dp[x][0], dp[x][0]);
	if (dep[x] < dep[y]) swap(x, y);
	for (int i = 20; i; i--)
		if (dep[f[x][i]] >= dep[y])
			ans -= cost[x][i], mx = max(mx, dp[x][i]), x = f[x][i];
	for (int i = 20; i; i--)
		if (f[x][i] != f[y][i]) {
			ans -= cost[x][i] + cost[y][i];
			mx = max(mx, max(dp[x][i], dp[y][i]));
			x = f[x][i], y = f[y][i];
		}
	if (x != y) {
		ans -= cost[x][0] + cost[y][0];
		mx = max(mx, max(dp[x][0], dp[y][0]));
		x = f[x][0], y = f[y][0];
	}
	mx = max(mx, dp[x][0]);
	return ans + mx;
}

signed main() {
	memset(dp, -0x3f, sizeof(dp));
	ios::sync_with_stdio(false);
	cin.tie(0); cout.tie(0);
	cin >> n >> q;
	for (int i = 1; i <= n; i++) {
		int x; cin >> x;
		c[i] = dp[i][0] = x;
	}
	for (int i = 1; i < n; i++) {
		int x, y, z; cin >> x >> y >> z;
		add(x, y, z); add(y, x, z);
	}
	init();
	while (q--) {
		int x, y; cin >> x >> y;
		cout << lca(x, y) << endl;
	}
	return 0;
}